Catalytic Steam Gasification Of Biomass For Hydrogen-rich Syngas Production

Most of countries are shifting energy profiles to renewable and sustainable resources due to environmental and economic incentives such as rising energy prices and depletion of fossil fuels.There are many technologies based on alternative energy sources.One of the important technologies is the gasification of biomass.The chemical differences in the structural components of biomass?cellulose and lignin?directly affect its chemical reactivity,thus affecting the characteristics of biomass gasification.Furthermore,CO₂ is a by-product in the gasification which is considered as a greenhouse gas that causes global warming.CO₂ can be absorbed by solid sorbents such as CaO and the H₂ content can get increased.H₂ produced by biomass gasification can be regarded as a high-level development of this renewable energy,and it is likely to play an important role in maintaining the future H₂ energy economy.The purpose of this study was to evaluate the effects of biomass components?cellulose and lignin?on gasification products and to evaluate the performance of CaO based sorbents in gasification process for H₂ rich syngas production.Specifically,the research investigated the gasification properties of biomass for H₂-rich gases in the presence of CaO based sorbents.The syngas compositions and product distribution were compared for gasification of lignin,cellulose,simulated and actual biomass enriched with lignin and cellulose.The influence of lignin and cellulose on the catalytic activity of CaO was identified,and the effects of ZrO₂ and CeO₂ on the performance of Fe/CaO in biomass gasification were investigated.Besides,the chemometric modeling on element compositions and product distributions of cellulose and lignin were also carried out.The main research contents are summarized as follows:Biomass components at the optimum CaO loading were gasified at different temperatures ranging from 600 to 800?,and then actual and simulated biomass feedstocks were gasified at optimum observed temperature.It was observed that increasing the CaO/cellulose ratio from 0 to1.5 enhanced H₂ improvement.In contrast,the hydrogen yield in lignin gasification slightly reduced when CaO/lignin mass ratio was more than 1.Maximum H₂ concentration was achieved with their corresponding CaO loading ratio at 650? in both the components.The gas evolutions trend from actual and simulated biomass results were similar to those selected biomass components.The effects of biomass components?cellulose and lignin?on CaO catalyst were investigated in biomass gasification.Cellulose,lignin and two types of biomass were chosen for this study:corn stover and walnut shell.They represent biomass with a high cellulose and a high lignin contents,respectively.The results showed that cellulose and lignin displayed higher liquid and CO₂ yields,respectively.The characterization results showed that the tar from cellulose led to the formation of coke,caused the worthless rearrangement of catalyst crystals and reduced the specific surface area which could dramatically affect the catalyst activity in a repeated cycle.Furthermore,the XRD results exhibited that CaO and CaCO₃ peaks were more intense in the solid residues of corn stover and walnut shell,respectively.Higher CO₂ yield increased the carbonation of CaO in walnut shell gasification,which led to the formation of CaCO₃.In contrast,the CaCO₃ peaks reduced in the solid residue of corn stover gasification;this could be due to interaction of liquid?tar?with CaO,resulting in the suppression of the CO₂ capture capacity.In order to enhance the biomass conversion and hydrogen production,the additive effects of ZrO₂ and CeO₂ to Fe/CaO catalysts prepared by the impregnation methods were investigated in the steam gasification of lignin.Firstly the effects of Fe/ZrO₂ and Fe/CeO₂ loading contents on the catalytic performance were examined and then the optimum ratios of Zr-Fe/CaO and Ce-Fe/CaO catalysts were compared with Fe/CaO catalyst.Of these three catalysts for biomass conversion and hydrogen gas production,the performance was Zr-Fe/CaO>5Fe/CaO>Ce-Fe/CaO.This study revealed that the addition of ZrO₂ on Fe/CaO improved the catalytic activity on syngas yield,carbon conversion,cyclic stability,and displayed considerably higher H₂ yield with less residual char than from tests performed with other two catalysts.The CeO₂ modified Fe/CaO catalyst exhibited poor catalytic performance.The characterization results showed that the Zr-Fe/CaO catalyst exhibited higher resistance to sintering and less coke formation in the residue.Furthermore,the addition of ZrO₂ on Fe/CaO seemed to play a positive role in the stabilization of Ca₂Fe₂O₅crystals in the catalyst.In stability test,ZrO₂ modified Fe/CaO catalyst showed obvious catalytic activities and gave a nearly constant rate of hydrogen generation in all ten cycles,suggesting an excellent catalytic stability of this catalyst.The literature-based data on elemental properties,syngas compositions,and product distributions were assessed from pyrolysis and gasification process fueled with cellulose,lignin,cellulose-rich and lignin-rich biomass with the application of principal component analysis?PCA?.Two data sets?SET1&SET2?were created for element properties and product distribution,respectively.SET1 contained five variables including carbon?C?,hydrogen?H?,oxygen?O?,volatile matter?VM?,and fixed carbon?FC?.Whereas,SET2 represented syngas compositions and product distributions including H₂,CO₂,CO,CH₄,syngas,liquid and solid product.The datasets were analyzed:?a?to evaluate the variations in element compositions,?b?to characterize syngas and product distribution produced from thermochemical conversion processes,and?c?to verify which element properties have a more decisive effect on the variation of product distribution of selected feedstocks.PCA results on the SET1 reveal that the variation trends in element composition of cellulose and lignin is similar to those of the cellulose-rich and the lignin-rich biomass,respectively.Furthermore,carbon,oxygen,volatile matter and fixed carbon had the most significant role in differentiating selected feedstocks.PCA results on the SET2 exhibited the correlation among H₂,CO₂,CO and CH₄ in accordance with the methane reforming and water-gas shift reactions.Furthermore,the literature base-data showed that cellulose produced a higher liquid product than that from lignin due to high contents of volatile matter in cellulose,whereas lignin displayed higher solid product than that from cellulose due to the presence of high content of fixed carbon in lignin.The similar observations were found for cellulose-rich and lignin-rich biomass feedstocks,indicating that cellulose-rich and lignin-rich biomass are suitable for liquid?bio-oil?and solid?biochar?production due to high contents of VM and FC,respectively.